Physically unclonable functions (PUF) are identifiers on integrated circuits (“chips”) that result from process variation. Although these process variations may be undesirable for manufacturing, these process variations create a natural output, a unique “fingerprint” for each chip. By being able to identify a chip, security protocols can be built using the chip's “fingerprint”. For example, a PUF allows a user to present a challenge, where the PUF is designed to supply a large number of values.